A Honeycomb-Like Porous Crystalline Hetero-Electrocatalyst for Efficient Electrocatalytic CO 2 Reduction.

Porous heterostructured electrocatalysts with multifunctionality and synergistic effect have much benefit for efficient electrocatalytic CO 2 reduction reaction (CO 2 RR), yet it still remains a daunting challenge to explore heterostructures based on covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) in this field. Here, a series of honeycomb-like porous crystalline hetero-electrocatalysts (MCH-X, X = 1-4, X stands for the numbered sample obtained from different MOF doses in the synthesis of the MCH) are synthesized, and these are successfully applied in electrocatalytic CO 2 RR. The specially designed heterostructures with integrated porous MOF-template and ultrathin COF-coating enable efficient CO 2 adsorption/activation and conversion into CH 4 . The best of them, MCH-3, shows greatly inhibited H 2 evolution, excellent current density (-398.1 mA cm -2 ), and superior FE CH 4 ${\rm{F}}{{\rm{E}}_{{\rm{C}}{{\rm{H}}_4}}}$ (76.7%) to the physical mixture (38.0%), the MOF@COF without the honeycomb-like morphology (47.7%), and the bare COF (37.5%) and MOF (15.9%) at -1.0 V. Based on the density functional theory calculations and various characterizations, the vital roles of the MOF in facilitating CO 2 adsorption/activation, stabilizing intermediates, and conquering the energy barrier of rate-determining step are intensively studied.